Adhesion additives are known throughout the automotive coatings industry. Adhesion additives are often used as components in primer surfacers, or other intermediate coating compositions, to promote adhesion between a substrate and a topcoat system for an automobile, such as a topcoat system including a flexible basecoat and flexible clearcoat. In general, plastic substrates may be coated with curable, or thermosettable, coating compositions. Color-plus-clear composite coatings have been particularly useful as topcoats for which exceptional gloss, depth of color, distinctness of image, or special metallic effects are desired.
As largely used in primer surfacers, adhesion additives are typically solvent-borne primer surfacers, but may also be used in water-borne primer surfacers, that are applied to a bumper, i.e., facie, or other trim component as the substrate. Typically, these substrates are made up of thermoplastic polyolefin (TPO), and without the inclusion of an adhesion copolymer in an intermediate solvent-borne primer surfacer layer, the topcoat system may delaminate from the TPO substrate.
One kind of adhesion additive includes olefin-based based polymers or copolymers that have an olefin block that is substantially saturated and at least one (poly)ester or (poly)ether block. The olefin-based block polymer or copolymer is typically present in an organic solvent such as xylene, toluene, and the like. The individual components of the adhesion copolymers, i.e., the olefin-based polymer or block copolymer, frequently settle out into the organic solvent. This settling renders the adhesion composition unstable, i.e., having poor shelf stability, and therefore not suitable for use as a component of a solvent borne primer.
It has been found that the conductivity of wet paint and dry film coatings influences the transfer efficiency of adhesion promoters and topcoats, respectively. In order to obtain high transfer efficiency of an adhesion promoter on a typical plastic component with a very high resistivity, large amounts of polar solvents, often in an amount from about 5 to 25% based on formula weight, have typically been used to adjust the conductivity.
It is desirable to provide a coating composition without the addition of large amounts of polar solvents, that yet has a more stable adhesion promoter component of the coating composition that provides improved physical properties, including improved adhesion under harsh testing conditions and improved conductivity to allow for more efficient electrostatic spray applications.